High Alumina Cement (HAC) was popular up until to mid 1970’s due to its ability for rapid strength, in the mid 1970’s there were several roof collapses attributed to poor construction or chemical attack combined with the use of high alumina cement.
HAC is made with calcium aluminates rather than calcium silicates as used in ordinary Portland cement. Under certain climatic conditions mineralogical ´conversion´ can occur causing a loss of strength or susceptibility to chemical attack.
Therefore there are two main concerns with concrete cast in the fifties, sixties and parts of the seventies:-
One was the use of High Alumina cement (HAC) which can cause conversion problems in certain conditions of use, reducing strength.
The other major problem of the time up until 1977 when it was banned was the permissible use of calcium chloride in the concrete for advancing the rate of hardening. The use of this material could cause corrosion of embedded steel causing damage to the concrete units particularly if the steel was misplaced.
Therefore, many buildings built before 1977 require a certificate of sampling and testing during the prosses of conveyancing or mortgages.
The test for HAC is carried out with strict reference to the BRE recommended tests below and a certificate of test and sampling issued.
BS 1881 Part 124 and IP21/86 & BS4551/2005+A2:2013 with interpretation to BRE Digest 444 Part 2. Chlorides to Volhards method, and Building Research Establishment Special Digest ‘SD3’ for ‘detecting high alumina cement concrete’.